Morton said agents also were in the city this week to crack down on the sale of counterfeit merchandise before Sunday's Super Bowl between the San Francisco 49ers and Baltimore Ravens.

"This just takes good old-fashioned police work, people getting out on the streets," he said.

This is the fifth consecutive year that federal authorities have launched a similar operation to crack down on the sale of counterfeit sports goods. Roughly $5.1 million in goods were seized during the previous one, Morton said.

"This is the largest number we've ever seized," Morton said of the $13.6 million.

Morton said copycat websites selling bogus merchandise have become increasingly sophisticated in their efforts to dupe customers into believing they're purchasing licensed, official sportswear.

"The prices are not ridiculously low. They're just discounted enough to fool the consumer," he added.

Andy Hageman, owner of House of Football, an Albuquerque store that sells authentic, licensed NFL products, said every week he gets customers who find out that they had purchased fake jerseys online or at other stores. "They ask me to see if the shirt is a fake, and I usually can tell right away," said Hageman.

The quality counterfeit jerseys also vary, federal officials say. Authentic jerseys can usually be identified by the required NFL hologram logo and the high quality stitching, officials said.

"Sometimes, you can't even tell they are fakes," said Abar. "Other time, the jerseys have 'Patriots' misspelled."

Anastasia Danias, the NFL's vice president for legal affairs, said fans also need to be wary of buying counterfeit Super Bowl tickets from "any suspicious sources."

"We learn of hundreds of fans every year who travel to the host city with the hope of watching their team play in the Super Bowl game only to be turned away at the gate, having bought counterfeit tickets or tickets that were reported lost or stolen," she said.